Patrick W. Rappold John R. Carter
Dept. of Speech Pathol. and Audiol., Univ. of South Alabama, 2000 University Commons, Mobile, AL 36688
Most CDD and comodulation masking release (CMR) studies employ only two conditions; a correlated condition and an uncorrelated condition. Temporal envelopes of noise bands are identical in the correlated condition and degree of envelope correlation is the same (r=1.0) across trials within this condition. In the uncorrelated condition envelopes of the noise bands are not identical, but degree of envelope correlation fluctuates across trials within this condition. Thus, reported thresholds for correlated conditions represent the average threshold at a single degree of correlation, whereas reported thresholds for uncorrelated conditions represent the average threshold across various degrees of envelope correlation. In this study thresholds are determined for signal bands centered at 2000 Hz, in the presence of cue bands centered at 1500 Hz, at specific degrees of temporal envelope correlation (r=1.0, 0.75, 0.60, 0.50, 0.40, 0.25, 0.0, -0.25, -0.35). Thresholds at r=1.0 and 0.75 are about 10 dB higher than thresholds at r=0.25, 0.0, and negative degrees of correlation. Thresholds at r=0.50 are about 5 dB less than thresholds at r=0.75 and above, and about 5 dB greater than thresholds at r=0.25 and below. Thresholds at r=0.60, 0.50, and 0.40 are nearly equivalent. These findings suggest that at least three conditions (ranges of correlation) should be employed in CDD, CMR, and other studies investigating the influence of envelope correlation.